This invention relates to a novel class of azourethane and urea derivatives which are useful as organic gellants for grease formulations. More particularly, this invention is directed to certain arylazoarylurethane and arylazoarylurea compounds prepared by reacting an azophenol or azoamine with an isocyanate, which are excellent thickening agents for greases employed in high temperature applications.
In modern practice, it has become increasingly important that grease compositions be able to provide adequate lubrication at high temperature, e.g., temperatures of 350.degree. F. to 450.degree. F. or higher. In this regard, a variety of thickening agents have been proposed for use in such high temperature applications including soap base thickeners, inorganic clay thickeners and organic thickening agents. Of these classes of thickening agents, the organic thickeners, specifically those containing urea or ureido functional groups, have been considered quite attractive because of this ashless nature and high temperature thickening properties. Examples of such organic thickening agents include polyureas and ureido compounds as well as dibenzimidazole-diureas and related arylcarbamyl thickeners. These organic thickeners are generally prepared by reacting one or more mono-, di- or polyamines with one or more mono-, di- or polyisocyanates, with the synthesis scheme in the case of the arylcarbamyl compounds involving the reaction of an aromatic amine with the reaction product of an aromatic diisocyanate and p-aminobenzoic acid.
While organic thickening agents of the aforementioned types produce greases having desirably high dropping points, this is but one measure of a grease's ability to perform satisfactorily at high temperatures. Other important properties include thermal and mechanical stability, high temperature bearing performance, oxidation and corrosion resistance, etc. While additives are normally incorporated into grease compositions to improve one or more of these properties, the thickening agent itself can significantly affect, either favorably or adversely, the properties of the finished grease product. Thus, in spite of the numerous organic thickening agents known in the art, there is a continuing need for the development of thickening agents which will not only produce greases having high dropping points, but which will additionally augment other important properties of the finished product. The present invention provides such a class of thickening agents.